Diffusion transfer process



United States Patent f 3,211,551 DIFFUSION TRANSFER PROCESS RudolfWendt, Hamburg, Germany, assignor to Lumoprint Zindler KG., Hamburg,Germany No Drawing. Filed Feb. 10, 1960, Ser. No. 7,841 11 Claims. (Cl.96--29) This invention relates to photographic developing and copyingprocesses and is more particularly concerned with a novelcontact-copying material and a method for its manufacture for producingcorrectly sided positive images from exposed photographic emulsionlayers. The invention, moreover, provides for a new process forproducing such positive images by employing the novel contact-copyingmaterial.

The invention is applicable to the production of positive images fromall kinds of exposed photographic, silverhalide containing emulsionlayers comprising additional developing substances.

In known photographic diffusion processes, generally, a latent image isfirst produced by exposure of a photographic layer, whereupon this imageis developed in contact with a gelatine layer containing reductionnuclei, preferably colloidal silver, by dissolving the unexposedsilver-halide in the photographic layer.

It is also known to cause and initiate such a diffusion by the action ofheat, in which case substances are added to the. corresponding layerswhich, upon heating above their melting point, split off water ofcrystallization. Such a water-yielding substance (i.e. a hydrate) is,for example, crystallized sodium sulphate. The water of crystallizationliberated during the heating referred to dissolves the developingsubstances and fixing agents, so that the development and fixing arecaused merely by heating. In prior methods of this kind gelatine wasused which is reversible so as to absorb part of the liberated water ofcrystallization by its own swelling.

Furthermore a method for producing embossed pictures by heating is knownin which the heat acts upon the developers having tanningcharacteristics. This method also uses gelatine for both the negativeand positive layers.

It is a primary object of this invention to overcome the drawbacks ofknown processes of the kind referred to, and to provide a novel contactmaterial which, merely upon being pressed while heated against anexposed photographic layer, will result in the formation of a correctlysided positive image on the material corresponding to the latent imageon the exposed photographic layer.

A further object of the invention resides in the provision of a processfor producing correctly sided positive images from exposed photographiclayers.

It is also an object of this invention generally to improve onphotographic contact-copying processes and photographic contact-copyingmaterial and methods for their manufacture as presently practiced andused.

Briefly, in accordance with this invention, correctly sided positiveimages are formed by pressing against the exposed film layer a positiveor transfer layer comprising polyvinyl alcohol and a hydrate, such assodium acetate, capable of yielding water of crystallization. Polyvinylalcohol upon heatingin contrast to gelatine-is not reversible uponabsorption of water.

According to a preferred embodiment of the invention,

the polyvinyl alcohol layer comprises, in addition to the 3,211,551Patented Oct. 12,1965

ice

water-releasing substances, also bifunctional or trifunctional alcoholswhich assure a high residual moisture and at the same time act asreducing agents.

It is essential for the successful operation according to the inventionthat the positive layer is not formed by re-v versible gelatine, butthat polyvinyl alcohol isused, and that this transfer layer does notcontain colloidal silver.

Polyvinyl alcohol if used as a layer-forming substance will liberate thebound water of crystallization much better than the known layersubstances, e.g., gelatine. Advantageously, sodium acetate is added tothe polyvinyl layer as a deliquescent thermally activable hydrate. Theamount of sodium acetate is chosen in such a manner that, during use andupon heating, an amount of water is liberated which is required toenable the activation of the developing agents in the negative layer andthe diffusion of the silver salt from its unexposed areas into thepositive layer. Besides sodium acetate, sodium citrate and sodiumsulphate can be used. Preferably, glycerol is added as a reducing agent.In a positive layer formed in this way the presence of colloidal silveris superfluous.

The negative layer, from which the image is to be transferred, maycomprise any desired silver-halide emulsion, for example,silver-chloride and silver-bromide emulsion in varying mixtures, havinga high or low sensitivity with any desired gradations and with a normal,increased or decreased content of silver. The commonly knownphotographic developing substances are added to the negative emulsionlayer. As developing substances can be used: methyl paminophenol-sulphate, paraphenylenediamine and its derivatives andhydroquinone. The following alkali substances may be used: sodiumcarbonate and caustic soda.

Advantageously, heating presses, electrically heated high-gloss presses,drum dryers, or the like may 'be used for the developing and thesimultaneous transmission of the image to the positive layer. Thetemperature is chosen so that it remains below the hardening point ofthe positive layer. Generally, a working temperature of -80 C. isadvantageous, but this of course is dependent on the positive-layercomposition, hence I wish not to limit myself to this temperature range.Advantageously, the invention includes a temperature range from 70 to120 for operation. Advantageously, the press has a pressure of 0.5-1.0kg./m.

The positive layer is applied onto a carrier sheet or strip such aspaper, plastic or the like. It is of course within the scope of thisinvention to coat the carrier material with positive layers on bothsides. In this case and during developing by heat the carrier coated onboth sides will be placed between two negative layers so that a copy oneach side is obtained in a single step. According to a preferredembodiment, substances may be added to the positive layer which willfurther and enhance the development of the negative layer. Suchadditives may include, for example, alkali-metal salts such as sodiumcarbonate and substances which facilitate the conversion of theunexposed silver halide into a soluble complex compound, such as sodiumthiosulphate. Preferably, the deliquescent hydrates are added, withreference to the polyvinyl alcohol, in amounts of about -200%.Furthermore, conventional hardening agents as well as additives forpreventing yellowing and achieving improved blackening and contrast maybe added to the positive layer.

The invention will now be described with reference to the followingexamples, it being understood, however, that these examples are given byway of illustration and not of limitation and that many alterations maybe made in, e.g., quantities, choice of material and operatingconditions in general Without departing from the scope and spirit ofthis invention as described in the appended claims.

Example 1 10 g. of polyvinyl alcohol are stirred with 20 ml. of glycerolin a porcelain dish until a homogeneous paste is formed. A solution of 2g. of sodium carbonate in 50 ml. of water is added to this paste underconstant stirring. The mass thus otbtained is then heated to SO -100 C.and 15 g. of sodium acetate in solid form is added. After the sodiumacetate is completely dissolved, the mass is coated onto a carrier suchas paper, whereupon the layer is dried.

Example 2 A positive layer is prepared as in Example 1, with the furtheraddition of 1 g. of sodium thiosulphate to induce the unexposed silverhalide of the negative layer to form soluble complex salts.

Example 3 A positive layer is prepared as in Example 2 with the furtheraddition of 0.2 g. of benztriazole for increasing the blackening effectof the reduced silver in the positive layer.

Example 4 A positive layer is prepared as in Example 2 with the furtheraddition of 0.2 g. of potassium metabisulphite to increase thedissolving action of the sodium thiosulphate.

Example 5 A positive layer is prepared as in Example 4 with the furtheraddition of 0.2 g. of sodium bicarbonate to minimize yellowing.

In all examples, a sheet of paper or plastic material is used as thecarrier. The carrier material should advantageously be water-repelling.

Example 6 A coated carrier sheet obtained according to any one ofExamples 1-5 is placed against an exposed photographic emulsion layer,e.g., an exposed film, containing common developing substances. Pressureand heat are applied. The temperature should be about 70-80 C. The imageappears on the positive layer after a short time.

However, it is pointed out that the temperature depends on the hardeningdegree of the negative layer and may thus vary in accordance with thecomposition of this layer. The duration of the heating depends on thenature and amount of the water-liberating substance used in the layer.

The concept of using polyvinyl alcohol as layer-forming material inpositive contact-copying material is entirely novel and the beneficialresult obtained thereby is certainly surprising and unexpected.

I claim:

1. A process for producing positive contact copies from an exposednegative provided with a photographic emulsion layer containing a silverhalide and a developer therefor, comprising the steps of placing saidemulsion layer in contact with a transfer layer of polyvinyl alcoholdevoid of colloidal silver and containing a hydrate thermally activableto release bound water, said transfer layer further containing awater-retaining reducing agent and a solvent for silver halide; andheating said layers to a temperature not exceeding 100 C. but sufficientto liberate water from said hydrate with resulting activation of saiddeveloper, difiusion of a solution of undeveloped silver halide fromunexposed portions of said emulsion layer into said transfer layer andreduction of the diffused silver halide whereby a positive image isproduced in said transfer layer.

2. A process for producing positive contact copies from an exposednegative provided with a photographic emulsion layer containing a silverhalide and a developer therefor, comprising the steps of placing saidemulsion layer in contact with a transfer layer of polyvinyl alcoholdevoid of colloidal silver and containing a hydrate thermally activableto release bound water, said transfer layer further containing awater-retaining reducing agent, an alkalimetal salt and a solvent forsilver halide; and heating said layers to a temperature not exceeding100 C. but sutficient to liberate water from said hydrate with resultingactivation of said developer, diffusion of a solution of undevelopedsilver halide from unexposed portions of said emulsion layer into saidtransfer layer and reduction of the diffused silver halide whereby apositive image is produced in said transfer layer.

3. A process for producing positive contact copies from an exposednegative provided with a photographic emulsion layer containing a silverhalide and a developer therefor, comprising the steps of placing saidemulsion layer in contact with a transfer layer of polyvinyl alcoholdevoid of colloidal silver and containing a hydrate thermally activableto release bound water, said transfer layer further containing awater-retaining reducing agent selected from the group which consists ofdifunctional and trifunctional alcohols and a solvent for silver halide;and heating said layers to a temperature not exceeding 100 C. butsufficient to liberate Water from said hydrate with resulting activationof said developer, diffusion of silver halide from unexposed portions ofsaid emulsion layer into said transfer layer and reduction of thediffused silver halide whereby a positive image is produced in saidtransfer layer.

4. A process for producing positive contact copies from an exposednegative provided with a photographic emulsion layer containing a silverhalide and a developer therefor, comprising the steps of placing saidemulsion layer in contact with a transfer layer of polyvinyl alcoholdevoid of colloidal silver and containing a hydrate thermally activableto release bound water, said transfer layer further containing awater-retaining reducing agent selected from the group which consists ofdifunctional and trifunctional alcohols, an alkali-metal salt and asolvent for silver halide; and heating said layers to a temperature notexceeding 100 C. but sutficient to liberate water from said hydrate withresulting activation of said developer, diffusion of a solution ofundeveloped silver halide from unexposed portions of said emulsion layerinto said transfer layer and reduction of the diffused silver halidewhereby a positive image is produced in said transfer layer.

5. A process as defined in claim 4 wherein said hydrate is selected fromthe group which consists of sodium acetate, sodium citrate and sodiumsulphate.

6. A process as defined in claim 4 wherein said reducing agent isglycerol.

7. A process as defined in claim 4 wherein said solvent is sodiumthiosulphate.

8. A process as defined in claim 4 wherein said alkalimetal salt issodium carbonate.

9. A process for producing positive contact copies from an exposednegative provided with a photographic emulsion layer containing a silverhalide and a developer therefor, comprising the steps of placing saidemulsion layer in contact with a transfer layer of polyvinyl alcoholdevoid of colloidal silver and containing sodium acetate, glycerol,sodium thiosulphate and sodium carbonate, and heating said layers to atemperature ranging substantially between 70 and C. to liberate waterfrom said sodium acetate with resulting activation of said developer,diffusion of silver halide from unexposed portions of said emulsionlayer into said transfer layer and reduction of the diifused silverhalide whereby a positive image is produced in said transfer layer.

10. A process as defined in claim 9 wherein the proportion of sodiumacetate ranges substantially between 100% and 200%, by weight, of thepolyvinyl alcohol.

11. A process as defined in claim 10 wherein the sodium carbonate andthe sodium thiosulphate are present in quantities of the order ofone-tenth the weight of the sodium acetate.

References Cited by the Examiner UNITED STATES PATENTS 2,352,014 6/44Rott 96-29 2,412,200 12/46 Blum 26029.6 2,747,999 5/ 56 Yutzy et a1.96-29 2,878,121 3/59 Gray 96-29 2,971,840 2/61 Haydn et a1. 9629 6FOREIGN PATENTS 555,103 8/57 Belgium. 1,003,578 2/57 Germany.

614,155 10/48 Great Britain. 5 790,811 2/ 58 Great Britain. 801,053 9/58Great Britain.

OTHER REFERENCES Glafkides, Photographic Chemistry, Fountain Press, 10London, 1958, pages 150-154.

NORMAN G. TORCIHN, Primary Examiner.

MILTON STERMAN, PHILIP E. MANGAN, l5 Examiners.

1. A PROCESS FOR PRODUCING POSITIVE CONTACT COPIES FROM AN EXPOSED NEGATVE PROVIDED WITH A PHOTOGRAPHIC EMULSION LAYER CONTAINING A SILVER HALIDE AND A DEVELOPER THEREFOR, COMPRISING THE STEPS OF PLACING SAID EMULSION LAYER IN CONTACT WITH A TRANSFER LAYER OF POLYVINYL ALCOHOL DEVOID OF COLLOIDAL SILVER AND CONTAINING A HYDRATE THERMALLY ACTIVABLE TO RELEASE BOUND WATER, SAID TRANSFER LAYER FURTHER CONTAINING A WATER-RETAINING REDUCING AGENT AND A SOLVENT FOR SILVER HALIDE; AND HEATING SAID LAYERS TO A TEMPERATURE NOT EXCEEDING 100*C. BUT SUFFICIENT TO LIBERATE WATER FROM SAID HYDRATE WITH RESULTING ACTIVATION OF SAID DEVELOPER, DIFFUSION OF A SOLUTION OF UNDEVELOPED SILVER HALIDE FROM UNEXPOSED PORTIONS OF SAID EMULSION LAYER INTO SAID TRANSFER LAYER AND REDUCTION OF THE DIFFUSED SILVER HALIDE WHEREBY A POSITIVE IMAGE IS PRODUCED IN SAID TRANSFER LAYER. 